north-south asymmetry in the solar wind during recent and past solar cycles
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North-South Asymmetry in the Solar Wind During Recent and Past Solar Cycles. Bertalan Zieger Center for Space Physics, Boston University. Questions. Is the solar wind distribution symmetric to the solar equator? What causes the asymmetry? - PowerPoint PPT PresentationTRANSCRIPT
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North-South Asymmetry in the Solar Wind During Recent and Past Solar Cycles
Bertalan Zieger
Center for Space Physics, Boston University
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• Is the solar wind distribution symmetric to the solar equator?
• What causes the asymmetry?
• How does the north-south asymmetry change during the solar cycles?
• Is Solar Cycle 24 exceptional?
Questions
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Annual and Semiannual Variation in Solar Wind Speed
Zieger and Mursula, 1998
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Alternating Phase Between Spring and Fall
Zieger and Mursula, 1998
V
Kp
Bs
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Mursula and Zieger, 2001
North-South Asymmetry in Past Solar Cycles:SC 9 to 22 (Years 1840-2000)
V
aa
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North-South Asymmetry in Recent Solar Cycles:SC 20 to 24 (Years 1960-2014)
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Coronal Magnetic Field During CR 1642(June 1976)
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Harmonic Coefficients
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Axial Multipoles
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Polar Field Strength
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Quadrupole Field Configurations
Axial quadrupole:g2,0, g2,1, h2,1
Tilt angle:atan(g2,0/sqrt(g2,1
2+h2,12))
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Axial Dipole and Quadrupole Components
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Dipole and Quadrupole Tilts
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The Cause of the Solar Wind Asymmetry: Axial Quadrupole
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Superposition of a Positive Dipole Moment With a Negative Quadrupole Moment
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Superposition of a Positive Dipole Moment With a Positive Quadrupole Moment
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Crooker et al., 2007
Solar Wind Speed Map in Early 1995
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North-South Asymmetry in Helium Abundance
Kasper et al., 2007
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Conclusions
1. The latitudinal distribution of solar wind speed is asymmetric during solar minima.
2. The north-south asymmetry shows a systematic 22-year pattern.
3. The north-south asymmetry of solar wind speed is caused by the axial quadrupole component of the coronal magnetic field.
4. The oscillation of the axial quadrupole component is equivalent with a north-south oscillation of the solar dynamo center.
5. Cycle 24 is exeptional in that it brakes a century-long asymmetry pattern that has prevailed in the previous 7 cycles since 1930.
6. The Sun is currently approaching a grand minimum.